“Many of the considerations I have brought forward were stated by Mr. R. A. Proctor some fifty years ago; they have therefore been accessible to astronomers, who nevertheless have been, as a rule, quite unaffected by them, so that it is time to state them afresh. The consideration that the life of a short-period comet is limited by the rapid wastage to which it is subject by the joint action of the sun and Jupiter was not, I think, so fully realised, when Proctor wrote as it is now. It serves further to invalidate the capture theory, since it prevents our assigning to these bodies such extended lives as that theory demands.” According to my father’s theory, the giant planets are themselves the parents of their comet-families, and he pictured their birth as having occurred in a remote past, when the planets were more sun-like than they are to-day. We have a great amount of evidence as to the energy of the processes that are at work on Jupiter, as evidenced, for instance, by the great Red Spot (though some have hinted at the possibility of its being an early stage in the formation of a new satellite); Saturn, Uranus, and Neptune also indicate vast upheavals, though distance in their case hinders observation, and even on our own planet we have some striking instances of the power of volcanic energy, as at the eruption of Krakatoa in 1883. Sounds of the explosion were heard three thousand miles away, and a huge volume of dust was blown to the highest regions of the atmosphere, but we are entitled to expect much vaster convulsions in Jupiter, which outweighs the earth three hundred times and is in a much hotter state, judging by the deep envelope of vapours surrounding it, and the rapid changes that are constantly taking place in its appearance, on an enormous scale, as shown by the fine series of photographs which have been obtained of the planet with the giant telescopes. Writing in his magazine, _Knowledge_, for January 1, 1887, page 64, my father states: